Comparative aspects of cerebral cortical development

Abstract

This review aims to provide examples of how both comparative and genetic analyses contribute to our understanding of the rules for cortical development and evolution. Genetic studies have helped us to realize the evolutionary rules of telencephalic organization in vertebrates. The control of the establishment of conserved telencephalic subdivisions and the formation of boundaries between these subdivisions has been examined and the very specific alterations at the striatocortical junction have been revealed. Comparative studies and genetic analyses both demonstrate the differential origin and migratory pattern of the two basic neuron types of the cerebral cortex. GABAergic interneurons are mostly generated in the subpallium and a common mechanism governs their migration to the dorsal cortex in both mammals and sauropsids. The pyramidal neurons are generated within the cortical germinal zone and migrate radially, the earliest generated cell layers comprising preplate cells. Reelin-positive Cajal-Retzius cells are a general feature of all vertebrates studied so far; however, there is a considerable amplification of the Reelin signalling with cortical complexity, which might have contributed to the establishment of the basic mammalian pattern of cortical development. Based on numerous recent observations we shall present the argument that specialization of the mitotic compartments may constitute a major drive behind the evolution of the mammalian cortex. Comparative developmental studies have revealed distinct features in the early compartments of the developing macaque brain, drawing our attention to the limitations of some of the current model systems for understanding human developmental abnormalities of the cortex. Comparative and genetic aspects of cortical development both reveal the workings of evolution.

A Comparative Proteomic Analysis of Human and Rat Embryonic Cerebrospinal Fluid

“…25,26 At E17.5, a time period post-cortical plate formation, the lateral ventricles are still large enough to collect pure samples of CSF, and all layers of the ventricle from the ventricular zone, the subventricular zone, the intermediate zone, the subplate, the cortical plate, and the marginal zone are clearly visible. 25,26 CSF from two litters (approximately 20-24 rat embryos) was pooled for each time point and was separated by 1-D SDS-PAGE, and the proteins were visualized with Coomassie blue stain. Figure 1C shows the Coomassie stained protein pattern of CSF collected from all three time points.…”

“…E12.5 is approximately the same time period that the first post-mitotic neurons appear in the preplate just below the pial surface. 25,26 As the post-mitotic neurons accumulate in the preplate, they differentiate to become the subplate and the marginal zone during E14, with the first appearance of the cortical plate between the subplate and marginal zone at E15. 25,26 At E17.5, a time period post-cortical plate formation, the lateral ventricles are still large enough to collect pure samples of CSF, and all layers of the ventricle from the ventricular zone, the subventricular zone, the intermediate zone, the subplate, the cortical plate, and the marginal zone are clearly visible.…”

“…25,26 As the post-mitotic neurons accumulate in the preplate, they differentiate to become the subplate and the marginal zone during E14, with the first appearance of the cortical plate between the subplate and marginal zone at E15. 25,26 At E17.5, a time period post-cortical plate formation, the lateral ventricles are still large enough to collect pure samples of CSF, and all layers of the ventricle from the ventricular zone, the subventricular zone, the intermediate zone, the subplate, the cortical plate, and the marginal zone are clearly visible. 25,26 CSF from two litters (approximately 20-24 rat embryos) was pooled for each time point and was separated by 1-D SDS-PAGE, and the proteins were visualized with Coomassie blue stain.…”

Coevolution of radial glial cells and the cerebral cortex

“…The occurrence of basal progenitors in the dorsal pallium and their coalescence in the SVZ, which allows indirect neurogenesis and increased neuron production, has been widely recognized as the critical milestone in the evolutionary expansion of the cerebral cortex leading to mammals, particularly in its radial dimension and the formation of six layers (Cheung et al, 2010; Cheung et al, 2007; Molnar, 2011; Molnar et al, 2006; Puzzolo and Mallamaci, 2010), as originally proposed by Smart (1972a, 1972b). However, even with the occurrence of indirect neurogenesis, the persistence of aRGCs undergoing direct neurogenesis continues to limit neuron production because each neurogenic aRGC will generate, at most, half as many neurons compared with aRGCs generating basal progenitors; the difference will be even greater if basal progenitors can self‐amplify to any extent.…”

From sauropsids to mammals and back: New approaches to comparative cortical development

“…These observations suggest that the smaller number of cortical neurons in the radial domain is associated with the reduction and late appearance of the SVZ in marsupials. It also suggests that the cortical SVZ and the intermediate SVZ progenitors have been conserved across all mammals that have been studied (Molnár et al, 2006). …”